Information storage and retrieval is one of the major challenge faced in the past few decades. The challenge is to reduce the size of the data storage media and to increase the access time or data retrieval time. Although technical advancement has been made for the past few years, the mechanical motion of the disk and the optical head assembly using actuator mechanism imposes limitation on the size and density of the optical storage media. The mechanical rotation of the disk results in the wobbling effect of the rotating disk, which accumulates the tolerance limit. Thus a limitation is set on the size and the density of the storage media. Also, the resolution of the actuator movement limits the size and density of the storage media. Moreover, the mechanical movement of the disk and the actuator results in additional problems such as focusing error and tracking error. Therefore, the servo system becomes quite complicated since a feed back signal is required to compensate for tracking and focusing error. Due to limitation set in the resolution of the actuator and the wobbling effect of the rotating disk, it is not possible to reduce the spot size, the distance between the tracks and pitch size in the data storage media.
U.S. Pat. No. 4,550,249 discloses a method of deflecting the beam by using a mirror rather than moving the entire head assembly. The system includes an array of lenses, and each lens focuses the beam at least to one track. This array of lenses covers a substantial portion of the recording media and the deflecting mirror directs the beam onto the desired lens. The system is quite complicated in its design of making an array of lenses and also the means of deflecting the beam using a mirror leads to poor resolution. The error in the system will increase at higher scanning rate due to the vibration on the scanning mirror.
U.S. Pat. No. 4,918,679 discloses an apparatus by which grating is employed for deflecting the beam. The wavelength of the incident beam is varied to change the deflection angle of the diffracted beam from the grating. This system shows an alternative way of positioning the beam to the desired track by producing a tracking error signal.
In order to minimize the size of the disk without compromising on the storage capacity of the optical storage media the resolution of the beam movement should be increased and the wobbling effect of the disk should be minimized. Both the above mentioned facts can be minimized to the maximum limit by making the optical storage media stationary and involving non-mechanical scanning of beam.
Since the control system works in conjunction with reading and writing the data, the simplification of the control system by eliminating or minimizing the focusing and tracking error will maximize the access rate of the data storage media.
Another limitation imposed on the present system is to read as well as record data using the same optical storage system rather than individual one. Further, the system is complicated due to the fact that the beam spot size and power of the beam is not the same for read and write system.